1. Field of the Invention
The invention is directed to a stationary continuous casting mold, especially for casting steel, with an electromagnetic device having a plurality of stirrer elements which are arranged on the outer wall of the continuous casting mold at a distance from one another and are connected to an electric a.c. voltage in a corresponding phase position for generating a rotating electromagnetic force field.
2. Discussion of the Prior Art
Stationary continuous casting molds are suitable for carrying out the process of casting steel using the immersion pipe casting method, in which the immersion pipe extending into the continuous casting mold is immersed in the melt. It is known to influence the solidification in continuous casting of high-melting metals such as steel by generating rotating electromagnetic fields in the stationary continuous casting mold by means of stirring. A stirring device for stationary continuous casting molds with two component stirring devices which can be operated independent from one another and are arranged one behind the other in the casting direction on the outer wall of the continuous casting mold is known, for example, from German Reference DE-OS 38 19 492. For this purpose, the electromagnetic rotating fields are generated in the mold. This stirring device is intended, in particular, to achieve a uniform, finer microstructure of the cast strand, a uniform distribution of nonmetallic inclusions, an improved removal of heat, etc.
In order to generate the magnetic flux, the stirring device (Herrmann, E., "Handbuch des Stranggie.beta.ens [Continuous Casting Handbook]", Aluminium-Verlag GmbH, Dusseldorf 1958, pages 417-429") can be constructed, for example, from a plurality of electromagnets of horseshoe-shaped transformer plates which are arranged vertically or horizontally on the wall of the continuous casting mold. The magnetic induction flux passes from one leg of the horseshoe to the other through the liquid metal melt. In so doing, the molten metal conducted through the mold is subjected to a continuous mechanical convection current by means of the magnetic flux. The stirring device is operated so that the electromagnets whose magnetic field propagates, for example, in the direction of the vertical axis of the mold are controlled such that the direction of maximum magnetic flux rotates about the vertical axis of the mold. In this way, a good circulation of the molten metal is achieved with good efficiency at the same time.
However, there are various disadvantages to stirring the melt with a stirring device of the type mentioned above. In spite of the stirring, there is usually ebullition at the surface of the melt which causes casting powder and slag particles at the immersion pipe to be drawn into the casting shell region. A further disadvantage consists in persistent bridging of solidified metal between the ceramic inlet tube and the mold wall in the upper region of the continuous casting mold despite stirring. In this type of stirring, there is also a recurring backup of superheat in the inner region of the mold, which promotes the formation of dendrites which then usually accumulate at the liquid-solid interface or solidification front of the melt as globulites. Although a uniform solidification front can be achieved with the known device, strips with negative segregation are formed in the melt.